Method of producing a seal



Dec. 20, 1938.

R. B. GRAY r AL 2,140,672

METHOD OF PRODUCING A SEAL Filed April 17, 1937 INVENTOR. REID B.GRRY HRRRY M. SHEALEY ATTORNEY.

Patented Dec. 20, 1938 UNITED STATES-PATENT OFFICE LETHOD F PRODUCING A SEAL Reid B. Gray, Dundalk, .and Harry M. Shealey,

Baltimore, Md., assignors to The Glen L. Martin Company, Baltimore, Md.

Application April 17, 1937; Serial No. 137,505

Claims. (Cl. 189-36) I in the installation of windows, body seams, and so This invention relates to an improved seal and the method of producing the same.

In the construction of aircraft as well as other commercial products it has been found advanta- 5 geous, and in some cases necessary, to employ means for sealing one member to another that.

will not only be unaffected by such liquids as motor fuel oil and salt water, but which will be possessed of a required amount of pliability. Such a seal must also he possessed of sufficient adhesive characteristics to positively maintain a leakproof connection. 7

It can be readily understood that fuel tanks employed in aircraft are subjected to various and sundry stresses and strains, particularly so when such fuel tanks are built-in and form a part of an aircraft wing structure, hull structure, sponson struct e, and the like, and that unless the means e oyed for sealing the seams and joints in these structures are possessed of a required amount of pliability or plasticity, such seams will eventually become impaired to the extent of serious leaking. Likewise; a sealing means possessed of these same characteristics is desirable for sealing scams or joints in other portions of an aircraft, such as the body, window connections, and it is particularly desirable where glass is employed.

It is one object of this invention to provide means for sealing one member to another as well as a novel method of producing an improved seal.

Another object is to provide means for sealing one member to another which shall be possessed of a required amount of plasticity and have the characteristics of being unafiected by motor fuel, such as gasoline, lubricating oils, water, and the like.

Another object is to provide a novel method for sealing one member to another that shall produce 40 a pliable seal which will withstand the stresses and strains encountered by the structures of aircraft and the like.

Another object is to provide a seal and a meth- 7 0d of producing such seal that shall, in addition sealing seams in aircraft such as those required forth, that shall operate to prevent the leakage of air through such seams when the aircraft is operated at high altitudes and may be subjected to diflerential air pressures.

The above and other objects will be made apparent throughout the further description of the invention when taken in connection with the accompanying drawing. It is to be distinctly understood that the drawing is not a definition of the invention, but merely] illustrate certain forms by which the invention may be eflectuated. The invention will be defined by the appended claims.

In the drawing: 7

Figure 1 is a fragmentary sectional view illustrating a simple lap seam embodyingthe invention,

Figure 2 is a fragmentary sectional view illustrating another embodiment of the invention employing a fillet. I

Figure 3 is a fragmentary sectional viewillustrating another embodiment of the invention in connection with the installation of a window, and

Figure 1 is a fragmentary sectional view of another embodiment of the invention illustrating one manner in which the present sealing medium may beemployed as a corrosion inhibitor in an unaccessible crevice.

In a preferred embodiment of Ithe invention the sealing medium employed is known to the the thicker; of the two and, of course, contains less solvent. Thiokol C--20'7 is very similar to G20, except it appears to be of a slightly thicker consistency. The primary differences between Thiokol C-207 and Gl8 and 20 are that 0-207 is possessed of greater adhesive qualities and offers a greater resistance to cold-flow.

In the drawing, Figure 1 illustrates a simple lap connection, wherein Thiokol indicated at I0 is disposed between the lapped portions II and I2 of members l3 and M, respectively. The lapped portions II and [2 may be firmly secured together by means of rivets, bolts, and the like, as indicated at l5.

It is specifically pointed out here that the suc- 'cess of using Thiokol as a sealing medium is dependent upon the method used in producing the seal. In the case 01' a lapped seam, as described in connection with Figure 1, an initial prepara-' tory coat of Thiokol 6-18 should first be applied to the surfaces to be sealed and allowed to air-dry two hours and a second brush coat of slightly heavier consistency should be applied over the initial preparatory coat. This second coat should air-dry until tacky, this time may vary some twenty-five to forty minutes, before lapping sheets or plates for riveting. This is necessary in order to overcome a natural tendency of the sealing medium to cold-flow under pressure. Thiokol (3-207 is applied in the same manner as G--l8 and G20, except that the thin coats consist of thinning the -20! to the desired consistency.

Figure 2 illustrates one manner of applying a Thiokol fillet to a seam such as that formed by the lapped portions IS and ll of members i8 and i9, respectively. The Thiokol fillet indicated at 2i is best produced by applying a thin coat of Thioko1G-i8 to the surface and permitting such coat to dry for a minimum of twenty minutes, or longer if production permits. Thiokol (3-20 is then applied in the form of a fillet along the seam or joint as the case may be. The size or depth of this fillet is dependent upon the type of joint or seam to be sealed. The fillet should be dried by circulating air for a minimum of forty-eight hours before using any liquid in the compartment if such filleting is in a fuel compartment or tank.

When Thiokol scaling is used in connection with certain alloys, such as aluminum or polished steel, it is important that the surfaces of these alloys be treated in order that suitable adhesion will be obtained.

The method of treating aluminum or aluminum alloys for use with Thiokol consists in what is known by the trade as anodizing the surfaces of such alloys. Anodize is simply 'a trade-name which means that the metal to be treated is used as the anode in an electrolytic process. The pres ent process consists in subjecting the alloy surfaces to an electrolytic bath of chromic acid. Other methods such as a sulphuric bath may be employed. Ordinarily suitable adhesion cannot be obtained on untreated aluminum or aluminum alloys. Polished steel surfaces should be roughened by emery or other means.

In the production of a metal to metal seal such as aluminum or aluminum alloy, it is not only necessary that the surfaces to be sealed be properly prepared, such as by anodizing, but it is para-- mount that sufficient drying time between thecoats of Thiokol be allowed for permitting excess solvents to evaporate and the Thiokol, which is in the form of a synthetic rubber, to set up in the form of a flexible film.

Figure 3 of the drawings indicates one manner .in which an aircraft window pane 22 may be installed in a window channel or frame 23. The

' cooperating edge of the window pane 2'2 is inthe coat of Thiokol be permitted to set up for,

several minutes prior to assembling the. structure.

does not only act as a seal, but serves as a cor- 5 rosion inhibitor. Such unaccessible crevices frequently exist in such structures as the hull of flying boats, sponsons, and the like, and particularly where fuel tanks are built-in and form a part of such structures. It is diillcult to preclude seepage of salt water as well as the seepage of gasoline, the latter often containing lead which attacks the metal structure.

Thiokol Gi8 as received in original form is a heavy consistency and somewhat difiicult to handie by brushing, especially where a thin film is desired. A thinner may be employed such as trichlorethylene or chloroform to obtain the required consistency.

In order to obtain a satisfactory fillet of Thiokol along a riveted lap or butt seam, a thin coat of G-i8 should first be brushed along the seam, being sure to brush freely to permit any excess to penetrate into recesses. After this coat has dried to touch, not tacky, a second coat of (5-4 8, not thinned, should be applied. This coat should also be a heavy one and not brushed too heavily as would thin it out. The initial thin coat generally requires about thirty minutes to set to touch. The second, which is a heavy coat, should be allowed to dry not less than twenty-four hours, and where production permits, forty-eight to seventytwo hours before testing sealing properties with either liquid or air. The time required will, of course, depend upon ventilation and temperature during this period.

It is imperative that where it is necessary to apply G-i! or G20 in closed places where natural ventilation is ;poor that adequate artificial ventilation be provided while the operators are applying the same.

In the construction of a seam such as that illustrated in Figure 3 it may be advisable to apply Thiokol of sufilcient body and consistency that a sufiicient amount of the sealing medium I will be squeezed or forced out of theseam and lie adjacent the lap and automatically form. a sealing fillet, such as that shown at 35. In many cases G-i8 in itself has sufficient body to form a sealing fillet, but in some cases, such as a window and so forth, a heavier grade of Thiokol is required. For such cases, Thiokol 6-20 is recommended. However, where a fillet is'desired, it should be obtained by the use of a heavy grade of Thiokol applied as a fillet.

Thiokol G-20 is of a consistencysimilar to putty and in itself has very poor adhesion to metal or other smooth materials. To successfully use G-20 for sealing it is necessary to first apply a thinned coat of Gl8 to the parts or surfaces to be sealed. When this is set to touch,

G-2il may be applied and will form a satisfactosy bond with the thin coat of Gi8.

Thiokol will not bleed through or discolor aluminum paint when painted after drying. However, G-i8 will soften and destroy paint films when applied over the same.

No specific instructions for thinning can be given insofar as thinning should be done to provide a smooth ficw and maximum penetration when brushed.

It is important when adding a thinner that only small quantities of thinner be added and the compound stirred vigorously 'until theadded thinner is entirely taken up. Adding toogreat 7 a quantity of thinner at one time might cause acurdling or precipitation of the compound.

Thiokolthinner trichlorethylene is quite volatile and it will be necessary where cans are opened and in use all day to occasionally add a small amount of thinner as the compound becomes too thick for satisfactory application.

Thiokol is a reaction product obtained from the interaction of sodium polysulfide and ethylene dichloride,- and may be considered as being a type of a. polymerized material which results from the reaction of sulfur and a halogenized unsaturated hydrocarbon.

Thiokol may be described as one form of synthetic rubber and some grades of 'Ihiokol may or may not contain rubber as such and it is to be carefully noted that while the present invention may be utilized in connection with other grades of Thiolrolv as well as other compositions or synthetic rubber, that it is important that any grade of Thiokol or other equivalent synthetic rubber compounds do not contain more than to 8% of rubber as such, since natural rubber products are definitelyafi'ected by motor Iuels.

While I have illustrated this invention in connection with certain grades or classes of Thiokol it will be obvious to those skilled in'the art that any synthetic rubber compound possessed of the characteristics herein tabove pointed out would probably be an equivalent to Thiokoh We claim: I 1. A method of forming a sealed connection between two structural members, comprising applying artificial hydrocarbon-resistant rubber cement of relatively low viscosity to each of the members, permitting such cement to dry, and

then applying in fluid form an intervening layer of artificial hydrocarbon-resistant rubber cement of high viscosity for the purpose of sealing said members, saidstructural. members being mechanically secured together in assembled relation.

2. The method of forming a sealed connection between two structural members, comprising applying a coat of artificial hydrocarbonresistant rubber cement of relatively low viscosity to each of the opposed faces of the mem bers, permitting such coats to dry, then applying in fluid form a layer of artificial hydrocarhon-resistant rubber cement of relatively high viscosity to one of said first coats, bringing said members together with said layer in contact with the-second coat, and mechanically securing said members together in assembled relation.

3. The method of forming a sealed connection between two structural members, comprising mechanically securing said members together in assembled relation, applying artificial hydrocarhon-resistant rubber cement of relatively lowviscosity to each of said members adjacent a point where they are secured together, permitting such cement to dry, and then applying in fluid form an intervening layer oi. artificial hydrocarbon-resistant rubber cement of high viscosity for the purpose oi. sealing said members. 4. In a method as claimed in claim 1, said rubber cement containing less than 10% of rubber. I

5. In a method as claimed in claim 1, said rubber cement comprising Thiokol.

' REID B. GRAY.

HARRY M. SHEALEY. 

